The concentrated dye solutions of certain anionic dyes have been discussed in U.S. Pat. Nos. 3,963,418 and 4,014,646. In these cases high dye solubility in an aqueous medium is achieved by the use of an organic cosolvent and the avoidance of sodium cations. The stability of these solutions to dilution with hard water is assured by the addition of certain carboxylic acid bearing chelating agents to sequester those metal ions such as calcium and magnesium whose presence in hard water causes precipitation of the dissolved dye. In order to avoid introducing sodium ions it is suggested that these chelating agents be added in their free acid forms.
The use of the free acid forms of chelating agents to form metal complex dyes, particularly trivalent chromium complexes, has been discussed in U.S. Pat. No. 3,305,539. Although it is indicated that the chelate enhances solubility, it is readily apparent from the sodium hydroxide neutralization taught in the working examples that this enhanced solubility is associated with the formation of a particular structure complex and not the initial absence of sodium or potassium counterions.
Spray dried dye powder of selected anionic dyes diluted with substantial amounts of an anionic dispersant in which the cold water "solubility" has been enhanced by the addition of tetrasodium salt of ethylene diamine tetra acetic acid (EDTA) or glycine is disclosed in U.S. Pat. Nos. 4,465,491 and 4,487,610 and European Pat. No. 57,158. The "solubility" is evaluated by the presence or absence of residue on SS 1450 CV filter paper. Evidently, the "solutions" were not optically evaluated for the absence of observable particles. The filter paper is coarse enough to allow the passage of some particles which would be trapped by finer filter paper such as Whatman No. 2. What is actually obtained appears to be a readily "dispersible" powder, i.e. powder which forms a fine filterable dispersion on addition to limited quantities of cold water.
Also relevant in the present context are U.S. Pat. No. 4,567,171 which disclosed concentrated stable aqueous dispersions of anionic dyes, which contain certain dispersing agents, and U.S. Pat. No. 4,468,230 which relates to stable aqueous dispersions containing an anionic dispersant and an electrolyte. Further, U.S. Pat. No. 4,110,073 disclosed stable water dispersions of anionic dyestuff. U.S. Pat. No. 3,948,599 disclosed a water soluble dye formulation added to a melt of urea while U.S. Pat. No. 4,328,220 and GB 1,497,666 relates to a dye preparation having improved solubilities.
U.S. Pat. No. 4,673,410 which relates to anionic dye dispersion having enhanced cold water solubility upon dilution discloses adding to these water dispersion a chelating agent and a cation source.